This invention relates to an apparatus for the detoxification of exhaust gases in an internal combustion engine. The invention relates, more particularly, to an apparatus for the detoxification of the exhaust gases of an internal combustion engine provided with a fuel metering mechanism, especially a carburetor, which meters fuel corresponding to the air quantity, as measured by an air quantity measuring device, so as to achieve a slightly enriched fuel air mixture (air number .lambda. &lt; 1). The apparatus includes a secondary air pump, by means of which secondary air is admitted under the control of an oxygen sensor disposed within the exhaust system, and until such time as an optimum fuel-air mixture is reached, corresponding to a particular air number .lambda..
It has already been suggested to admit secondary air ahead of a catalyzer into the exhaust gases of the internal combustion engine and to control the amount of secondary air by means of an oxygen sensor exposed to the exhaust gases. From a point of view of automatic control practice, this solution has the advantage that the regulation lag time is relatively short, because the actual and nominal values are both measured and determined within the exhaust system. On the primary side of the internal combustion engine, only a slightly enriched setting of the fuel-air mixture is necessary which does not make great demands on control processes. However, this known technique has the disadvantage that the fuel consumption is relatively high which can have a major importance in the future due to the increasing fuel prices and because of the decrease of raw material reserves. The relatively long dead time, which occurs in arrangements in which the measurement of the actual value is done on the secondary side of the engine and the setting of the nominal value is done on the primary side, is disadvantageous only under small loads and at low rpms.